fixes #528 - Support podcasts in web client

MediaBrowser.Api/Playback/BaseStreamingService.cs

@@ -469,6 +469,8 @@ namespace MediaBrowser.Api.Playback
         /// <param name="audioStream">The audio stream.</param>
         /// <returns>System.Nullable{System.Int32}.</returns>
         protected int? GetNumAudioChannelsParam(StreamRequest request, MediaStream audioStream)
+        {
+            if (audioStream != null)
             {
                 if (audioStream.Channels > 2 && request.AudioCodec.HasValue)
                 {
@@ -478,6 +480,7 @@ namespace MediaBrowser.Api.Playback
                         return 2;
                     }
                 }
+            }
 
             return request.AudioChannels;
         }

MediaBrowser.Api/Playback/Progressive/AudioService.cs

@@ -6,9 +6,7 @@ using MediaBrowser.Controller.Library;
 using MediaBrowser.Controller.Persistence;
 using MediaBrowser.Model.IO;
 using ServiceStack.ServiceHost;
-using System;
 using System.Collections.Generic;
-using System.IO;
 
 namespace MediaBrowser.Api.Playback.Progressive
 {